Various types of combustion may be used in an internal combustion engine. For example, spark ignition (SI) of a homogenous mixture during the expansion stroke is one example method. This method relies on a timed spark from a sparking plug in order to achieve ignition within the combustion chamber of an air and fuel mixture. Another type of combustion may be referred to as homogeneous charge compression ignition (HCCI), which occurs when the temperature of the combustion chamber exceeds an autoignition temperature for the specific fuel resulting in autoignition. HCCI can be used to provide greater fuel efficiency and reduced NOx production under some conditions.
In some cases it may be desirable to enable the combustion cylinders of the engine to operate either in SI mode or in HCCI mode, and from time to time during operation, switch from one mode to the other, so as to obtain the benefits associated with the different combustion modes. The benefits obtained by mode switching may be somewhat offset, however, by temporary performance and/or efficiency losses occurring as a result of transitioning the combustion mode for all of the cylinders. The presence of SI and HCCI combustion modes also presents aftertreatment issues, due to the significant differences in HCCI and SI combustion.
The inventors herein have recognized that the presence of multiple combustion modes, the use of high manifold pressures in certain combustion modes, and/or the deployment of operating modes that are sensitive to air-fuel ratio changes can present challenges related to fuel vapor purging. For example, the uncertainties of vapor concentration and content in the fuel vapor purge entering the engine can affect autoignition timing, among other parameters.
Accordingly, in one aspect the present description provides for an internal combustion engine having a gasoline fuel injection system and a plurality of combustion cylinders. Each of the combustion cylinders is configured to receive gasoline from the gasoline fuel injection system and combust a mixture of air and gasoline in either a spark ignition mode or a sparkless homogeneous charge compression ignition (HCCI) mode. The internal combustion engine also includes a fuel vapor purge system fluidly coupled to the plurality of combustion cylinders, where the internal combustion engine is configured to operate in a first purge state, in which fuel vapors are permitted to be received from the fuel vapor purge system only into combustion cylinders that are operating in the spark ignition mode, and in a second purge state, in which fuel vapors are permitted to be received from the fuel vapor purge system into combustion cylinders operating in the spark ignition mode and into combustion cylinders operating in the HCCI mode. Such an engine provides the benefits of multiple combustion modes while making efficient use of evaporated fuel vapors. Further, it is possible to reduce uncertainties in auto-ignition timing, thereby enabling improved HCCI operation.
According to another aspect, the present description provides for an internal combustion engine having a plurality of combustion cylinders and a fuel delivery system. The plurality of combustion cylinders are configured to receive a mixture of gasoline and air and combust such mixture, where some of the combustion cylinders are configured to operate in a spark ignition mode, with the remaining cylinders being configured to operate in a compression ignition mode. The fuel delivery system is configured to supply gasoline to the combustion cylinders, and includes a fuel vapor purging system configured to selectively control delivery of evaporated fuel vapors from a fuel vapor purge source to the combustion cylinders. Furthermore, the fuel vapor purging system is configured to operate in a first purge mode in which evaporated fuel vapors are permitted to be drawn from the fuel vapor purge source into less than all of the combustion cylinders. This configuration similarly provides the benefits of multiple combustion modes while effectively handling the purge issues raised by multiple ignition modes and the presence of a compression ignition mode.